Device for applying a ventrally or dorsally directed translatory force in the area of a knee joint

ABSTRACT

The invention relates to a device for applying a ventrally or dorsally directed translatory force onto a lower leg in the area of the knee joint. The inventive device comprises a thigh bar and a lower leg bar device having a shorter and a longer bar arm. Both bar arms can be freely swiveled relative to the thigh bar. The two bar arms are disposed in such a manner that they can be swiveled relative to each other. A pretension of a spring device between the shorter and the longer bar arm has the effect that the bar arms are urged to carry out a swiveling motion relative to each other, thereby applying a ventrally or dorsally directed translatory force onto a lower leg fixation device in an area close to the knee.

The invention relates to a device for applying a ventrally or dorsallydirected translatory force onto a lower leg in the area of a knee jointfor treatment or follow-up treatment of knee instability, in particularcruciate ligament instability, as set forth in the preamble of claim 1.

In the field of knee instability, posterior cruciate ligament lesions inparticular pose considerable medical problems. Although there are wellproven surgical reconstruction procedures for posterior cruciateligament ruptures and other lesions of the posterior cruciate ligaments,the result of surgery has often deteriorated after a few months, or beenlost altogether, because the sutured or reconstructed ligament has beenstretched again in an undesired manner on account of the gravitationalforce of the lower leg which, with the patient lying on his back, actsin the dorsal direction. This leads to incorrect positioning of thetibia relative to the femur, as is indicated by broken lines in FIG. 1.By contrast, the solid lines in FIG. 1 show the tibia and the lower legin the normal state. The risk of this kind of incorrect positioning,i.e. dropping of the tibia relative to the femur, also arises of coursewhen a posterior cruciate ligament lesion is treated, not surgically,but by conservative methods.

In the case of anterior cruciate ligament instability, a problem whichmay occur is that the tibia comes to lie too far in the ventraldirection relative to the femur. This is especially the case when thearticular surface of the patient's tibia is inclined in such a way that,in the upright position in which the femur presses on the obliquearticular surface of the tibia, a force is exerted in the ventraldirection on the tibia. If the anterior cruciate ligament is unstable,the tibia in the area of the knee joint is displaced forward in anundesired manner, i.e. upward as shown in FIG. 1.

A device is already known for applying a ventrally or dorsally directedtranslatory force onto the lower leg in the area of the knee joint,which device is intended to counteract this undesired shifting of thetibia. This known device has thigh bars which are arranged medially andlaterally in the area of the thigh and which can be secured on the thighby means of a cuff. A swivel lever is mounted in an articulated mannerat the distal end of the thigh bars which are located laterallyalongside the knee, which swivel lever is pretensioned either in theventral direction or in the dorsal direction by means of a spring. Thisswivel lever engages under or over a bolt protruding laterally from alower-leg cuff in an area of the lower leg close to the knee. Dependingon how the pretensioning of the spring is directed, the upper end of thetibia is urged either in the ventral direction or the dorsal directionin order to counteract an undesired stretching of a damaged posterior oranterior cruciate ligament and an associated translatory displacement ofthe tibia in the dorsal or ventral direction. A problem with this knowndevice, however, is that the spring force on the lower leg means that apermanent force is exerted in the extension direction or flexiondirection, i.e. a torque which seeks to permanently extend or flex thelower leg. A free and unimpeded extension or flexion of the knee istherefore not possible with this known device.

Starting out from this, the object of the invention is to make availablea device of the type mentioned at the outset which, in a particularlyeffective way, prevents undesired displacement of the tibia in thedorsal direction or ventral direction and permits free mobility of theknee joint.

According to the invention, this object is achieved by the features ofclaim 1. Advantageous embodiments of the invention are described in thesubsequent claims.

The device according to the invention has the following features:

-   -   the lower-leg bar device has a shorter bar arm and a longer bar        arm, both bar arms being able to swivel relative to the thigh        bar,    -   the two bar arms are arranged so as to be able to swivel        relative to one another,    -   the shorter bar arm is coupled at its distal end to the fixation        device in an area close to the knee, whereas the longer bar arm        is coupled with its distal end to the fixation device in an area        farther away from the knee,    -   the pretensioning force of the spring device acts between the        shorter and longer bar arms in such a way that the bar arms are        urged to execute a swiveling movement relative to each other,        such that a ventrally or dorsally directed translatory force is        applied to the fixation device in the area close to the knee.

It is thus a characteristic of the device according to the inventionthat the spring force does not act between the thigh bar and thelower-leg bar device, but instead between the two bar arms which extendfrom the knee-joint area in the distal direction alongside the lower legand, because of their different lengths, are coupled to the lower-legfixation device with their distal ends at different locations. In thisway, a torque is exerted on the fixation device, and thus on the lowerleg, and urges the tibia, in the area close to the knee joint, eitherinto the ventral direction or the dorsal direction depending on thedirection of the spring force and the arrangement of the bar arms. Bycontrast, both lower-leg bar arms are mounted on the distal end of thethigh bar so as to be able to swivel freely relative to the thigh bar,i.e. no spring force acts between the thigh bar on the one hand and thetwo lower bar arms on the other. The patient is therefore able to flexor extend his knee without additional force being applied.

According to an advantageous embodiment, at least one of the bar armshas, at its distal end, an oblong hole into which a bolt of the fixationdevice protrudes, in order to couple the bar arm to the fixation devicein a longitudinally displaceable manner. This takes account of the factthat the distances between the swivel axis of the device and the twocoupling points where the lower-leg bar arms engage on the fixationdevice may vary depending on the swivel position of the fixation device.The longitudinally displaceable coupling of the at least one bar arm onthe fixation device thus does not obstruct the swiveling movement of thefixation device by means of the two bar arms. As an alternative to anoblong hole, however, it would also be entirely possible to place thebar arm concerned onto the relevant bolt only from one side, so thatthis bar arm presses against the bolt from one side.

The fixation device which can be secured on the lower leg is expedientlymade up of a half-shell, and the two bar arms are coupled to thehalf-shell at the two opposite end areas of the half-shell.

According to an advantageous embodiment, the spring device comprises aflat coil spring arranged in a spring housing which is secured on one ofthe bar arms and, together with the latter, can be swiveled relative tothe thigh bar. The center axis of the spring housing in this caseexpediently coincides with the swivel axis. This permits a particularlysimple and space-saving configuration.

It is also expedient if, for adjusting the desired translatory force,the pretensioning force of the spring device can be adjusted by means ofa toothed gear wheel located in the spring housing.

According to an advantageous embodiment, the lower-leg bar device ismounted in an oblong hole of the thigh bar so as to be displaceable onthe thigh bar. In this way, the lower-leg bar device can, in addition tothe swiveling movement, also execute a translatory movement relative tothe thigh bar and in this way can optimally follow the path of movementduring flexion and extension of the knee, without unpleasant tension orcompression stresses arising on the thigh cuff along the thigh. For thispurpose, the oblong hole expediently extends in the longitudinaldirection of the thigh bar.

The invention is explained in more detail below by way of example withreference to the drawings, in which:

FIG. 1 shows a schematic representation of a human leg in the area ofthe knee joint with femur and tibia, the lower leg and tibia being shownin the normal position and in a dorsally displaced position,

FIGS. 2 a to 2 c show side views of a first embodiment of the deviceaccording to the invention placed on the leg, with different anglesettings of the lower-leg bar arms in order to elucidate the function ofthe invention,

FIG. 3 shows an exploded view of the most important individual parts ofthe device from FIGS. 2 a to 2 c,

FIG. 4 shows a cross section through the device according to theinvention in the area of the spring housing,

FIGS. 5 a and 5 b show a plan view and side view, respectively, of thedriving toothed wheel for tensioning the spring,

FIGS. 6 a and 6 b show a plan view and side view, respectively, of thetoothed wheel for tensioning the spring,

FIGS. 7 to 9 show a plan view of the device according to the inventionfrom the planes VII, VIII and IX as indicated in FIG. 4,

FIG. 10 shows a side view of a second embodiment of the device accordingto the invention, said device being situated substantially in anextension position,

FIG. 11 shows the device from FIG. 10 in the flexion position,

FIG. 12 shows a side view and a longitudinal section through the nutused in the second embodiment, and

FIG. 13 shows a shortened side view of the thigh bar, with oblong hole,used in the second embodiment.

A thigh 1 with femur 2 and a lower leg 3 with tibia 4 can be seen inFIG. 1. Here, solid lines indicate the normal position of the lower leg3 and tibia 4, and broken lines indicate a dorsally dropped position ofthe lower leg 3 and tibia 4, as may arise in cases of cruciate ligamentinstability, because of the dorsally acting gravitational force when apatient is lying on his back.

FIGS. 2 a to 2 c show a device in the form of an orthosis with which aventrally directed translatory force counteracting the dropping of thetibia can be applied onto the lower leg 3 in an area close to the knee,so that dropping of the tibia 4 can be prevented from the outset, evenin cases of weakened cruciate ligaments, or so that a dropping of thetibia 4 can be rectified. The direction of the translatory force appliedby the orthosis is indicated here by the arrow 5. FIG. 2 a shows theorthosis fitted on a leg, where the lower leg 3 is in a dropped state.FIG. 2 b again shows the normal position of the lower leg, which isobtained by means of the translatory force applied by the orthosis. Thebroken lines and solid lines in FIG. 2 c once again indicate thepositions of the lower leg 3 and of the orthosis as shown in FIGS. 2 aand 2 b, to permit direct comparison of the two states.

In FIGS. 2 a to 2 c, only the bar arrangement located on one side of theleg can be seen. The entire orthosis, however, is made up of two suchbar arrangements which extend laterally and medially alongside the legand are arranged with mirror symmetry in relation to one another. It isalso conceivable, however, for such a bar arrangement to be provided onjust one side of the leg.

FIGS. 2 a to 2 c show a thigh bar 6 which can be secured on the thigh 1by means of a cuff 7. The cuff 7 is expediently made up of a half-shellwhich is placed on the front of the thigh and which can be fixed on thethigh 1 by means of straps 8 which are guided round the back of thethigh and have velcro-type fasteners. In the distal end area of thethigh bar 6, located laterally alongside the knee joint, a shorter bararm 9 and a longer bar arm 10 extending in the direction of the lowerleg 3 are mounted so as to be able to swivel.

The swivel axis is indicated by 11. Both bar arms 9, 10, which togetherare designated here as lower-leg bar device, are able to swivel freelyrelative to the thigh bar 6, i.e. no spring force acts between the thighbar 6 on the one hand and the lower-leg bar device on the other hand. Bycontrast, a spring force does act between the shorter bar arm 9 and thelonger bar arm 10, and this spring force seeks to turn the shorter bararm 9 counterclockwise and the longer bar arm 10 clockwise.

The two distal ends of the bar arms 9, 10 act on a fixation device 12consisting of a half-shell 13 which is arranged dorsally, i.e. in thecalf area, and which extends along the lower leg 3 in the distaldirection from an area close to the knee. The half-shell 13 is securedon the lower leg 3 by means of a retaining strap 14 which has avelcro-type fastener.

As can be seen from FIGS. 2 a to 2 c, the distal end of the shorter bararm 9 is coupled to a bolt 15 which protrudes laterally outward from thefixation device 12 in the end area of said fixation device 12 close tothe knee. For this purpose, the shorter bar arm 9 has an oblong hole 16into which the bolt 15 engages. The bar arm 9 is thus guided in alongitudinally displaceable manner on the bolt 15 by means of thisoblong hole 16.

At its distal end, the longer bar arm 10 is mounted so as to be able toswivel on a bolt 17 in a distal end area of the fixation device 12. Thehalf-shell 13 can thus be swiveled about the bolt 17, as is indicated bythe arrow 18. Because of the distance between the bolts 15 and 17 in thelongitudinal direction of the lower leg 3, the half-shell 13 thusexecutes a swiveling or tilting movement in the clockwise direction andthereby exerts the desired translatory force on the tibia 4 in theventral direction.

Referring to FIGS. 3 to 9, the structure of the bar arrangement shown inFIGS. 2 a to 2 c will now be explained in more detail below.

As can be seen from FIGS. 3 and 4, this bar arrangement comprises, inthe area of the bar hinge, a bowl-shaped spring housing 19 which isscrewed onto the proximal end area of the shorter bar arm 9 and istherefore connected fixedly to the latter.

The proximal end area of the shorter bar arm 9 is designed as a circulardisk 20 whose external diameter corresponds to the external diameter ofthe spring housing 19. The spring housing 19 and the bar arm 9 each havea central through-hole 21, 22, respectively, through which a screw 23can be guided. The screw 23 is provided with a thread onto which a nut24 can be screwed until it bears on the bar arm 9. The screw 23 and thenut 24 are thus secured in position relative to the spring housing 19and bar arm 9.

The nut 24 has a hexagonal head 25 and an axially protruding cylindricalcollar 26 with a smaller external diameter than the head 25. Thiscylindrical collar 26 serves as a rotation bearing for the thigh bar 6which, for this purpose, has, in its distal end area, a centralthrough-hole 27 whose diameter is adapted to the external diameter ofthe cylindrical collar 26. A friction-reducing disk 28, in particularmade of Teflon, is arranged between the thigh bar 6 and the shorter bararm 9. It will be seen that, by virtue of this arrangement, the shorterbar arm 9 together with the spring housing 19 can be swiveled freelyabout the swivel axis 11.

As will be seen from FIGS. 3 and 4, a spring in the form of a flat coilspring 29 is arranged inside the spring housing 19, this spring beingused to generate a pretensioning force acting between the shorter bararm 9 and the longer bar arm 10. As will be explained in more detailbelow, this flat coil spring 29 cooperates with a toothed wheel gearwhich is likewise arranged inside the spring housing 19 and which ismade up of a central toothed wheel 30 and of a peripheral drivingtoothed wheel 31 of smaller diameter meshing with said toothed wheel 30.The central toothed wheel 30, which is shown in more detail in FIGS. 6 aand 6 b, has a central, axial protrusion 32 which, along most of itslength, i.e. in the area 33, has a square cross section on the outside.The end area 34 of the protrusion 32 is, by contrast, cylindrical on theoutside and serves as a rotation bearing for the longer bar arm 10 (seeFIG. 10). The bar arm 10, which extends through a recess in thecircumferential wall of the spring housing 19, is thus able to swivelabout the protrusion 32.

The central toothed wheel 30 also has a central, axial bore 35 throughwhich the screw 23 can be guided. The screw 23 thus serves as a rotationbearing for the central toothed wheel 30.

As will be seen from FIGS. 3 and 8, the flat coil spring 29 is bent in asquare shape in its inner end area in such a way that it can be fittedwith slight play onto the square protrusion 32 of the central toothedwheel 30. The inner end of the flat coil spring 29 is thus secured in arotationally fixed manner on the protrusion 32. The outer end of theflat coil spring 29 is connected to an axially disposed coupling pin 36which is secured on the longer bar arm 10.

By means of this arrangement, the pretensioning force of the spring 29thus acts between the central toothed wheel 30 and the longer bar arm10. The pretensioning force of the spring 29 can in this case be alteredby turning the toothed wheel 30, this being effected via the drivingtoothed wheel 31. The driving toothed wheel 31 is turned manually usinga hexagon key which can be introduced through a bore 37 in the springhousing 19 and can be brought into engagement with a hexagon-shapedrecess 38 in the driving toothed wheel 31.

Undesired turning of the central toothed wheel 30 relative to the springhousing 19 is prevented by means of a catch 39 (FIGS. 3 and 7) which isin engagement with the teeth of the toothed wheel 30. The catch 39 ismounted (in a manner not shown) in the spring housing 19 in such a wayas to be able to swivel. A spring tongue 40, secured on a retaining bolt41 of the spring housing 19, presses on the catch 39 from outside insuch a way that its free end in normal circumstances remains inengagement with the teeth of the toothed wheel 30 and prevents thetoothed wheel 30 from turning back because of the pretensioning force ofthe flat coil spring 29. However, the spring tongue 40 can be liftedfrom the catch 39 by means of an eccentric 42, which eccentric 42protrudes through an opening 43 in the spring housing 19 and can thus beactuated manually. If the spring tongue 40 is lifted from the catch 39,a further spring tongue 44, which presses from outside on the oppositeend area of the catch 39, can disengage the catch 39 from the teeth, sothat the toothed wheel 30 can be turned back and the pretensioning forcecan be reduced. The spring tongue 44 is also secured on the springhousing 19 by means of a retaining bolt 41.

When the catch 39 is engaged, the central toothed wheel 30 is thussecurely coupled in one direction to the spring housing 19 via thiscatch 39, and thus to the shorter bar arm 9. The spring force of theflat coil spring 39 thus acts, on the one hand, on the central toothedwheel 30 via the square protrusion 32 and, from the central toothedwheel 30, on the shorter bar arm 9 via the catch 39 and the springhousing 19, and, on the other hand, on the longer bar arm 10 via thecoupling pin 39.

In the illustrative embodiment shown, the flat coil spring 29 seeks toswivel the shorter bar arm 9 upward, i.e. counterclockwise, and thelonger bar arm 10 downward, i.e. clockwise, such that a translatoryforce is applied in the ventral direction to the tibia in the area closeto the knee. The device thus constitutes a so-called PCL bar. It will benoted that, alternatively to this, the application of a translatoryforce in the dorsal direction is possible in a simple way by reversingthe direction of action of the flat coil spring 29 and the catch 39, bywhich means the device can be used as an ACL bar.

FIGS. 10 and 11 show a second embodiment of the device according to theinvention in which the thigh bar 6, in the hinge area, has an oblonghole 46 extending in the longitudinal direction of the thigh bar 6. Thethigh bar 6 is shown on its own in FIG. 13. The oblong hole 46 meansthat the screw 23 serving as swivel axis, and thus the entire lower-legbar device, can move together with the spring housing 19 by a defineddistance along the oblong hole 46.

The nut 24 used in this embodiment is shown in FIG. 12. Like the nut inthe first embodiment, this nut 24 again has a cylindrical collar 26which engages in the oblong hole 46 and is guided by the long side wallsof the oblong hole 46 with slight play. The other parts of the secondembodiment are identical to those of the first embodiment and aretherefore not described again in detail here.

The way in which the second embodiment works is identical to that of thefirst embodiment. The shorter bar arm 9 is moved in the arrow direction(see FIGS. 2 a to 2 c) toward the longer bar arm 10 by the force of theflat coil spring 29. In this way, the half-shell 13, i.e. the lower-legshell, is swiveled about the distal coupling point 17 and pressedventrally in the end area close to the knee joint, such that the tibiais pushed forward relative to the femur.

This causes a reaction force which presses the end area of the lower-legbar device in the dorsal direction in the hinge area. Since the thighbar 6, however, is fixed securely on the thigh via the cuff 7, the hingearea of the device is held in a fixed position relative to the kneejoint. Upon flexion of the knee joint, however, the force acting in thehinge area seeks to displace the cuff 7 of the thigh slightly in theproximal direction. Upon subsequent extension, by contrast, a tensionstress, possibly felt to be unpleasant, would be exerted on the thighbar 6 if the lower-leg bar device were mounted non-displaceably on thethigh bar, as is the case in the first embodiment. However, the oblonghole 46, which is provided in the thigh bar 6 and is situated laterallyand centrally alongside the knee joint, permits a displacement of thebearing along the oblong hole 46, such that tension or compressionforces can be avoided in the longitudinal direction of the thigh.

1. A device for applying a ventrally or dorsally directed translatoryforce onto a lower leg in the area of a knee joint for treatment orfollow-up treatment of knee instability, in particular cruciate ligamentinstability, with a thigh bar which can be secured on a thigh, with alower-leg bar device which acts on the lower leg, is coupled in anarticulated manner to the thigh bar and is operatively connected to afixation device that can be secured on the lower leg, and with a springdevice which generates a defined pretensioning force and acts on thelower-leg bar device, characterized by the following features: thelower-leg bar device has a shorter bar arm and a longer bar arm, bothbar arms being able to swivel relative to the thigh bar, the two bararms are arranged so as to be able to swivel relative to one another,the shorter bar arm is coupled at its distal end to the fixation devicein an area close to the knee, whereas the longer bar arm is coupled withits distal end to the fixation device in an area farther away from theknee, the pretensioning force of the spring device acts between theshorter and longer bar arms in such a way that the bar arms are urged toexecute a swiveling movement relative to each other, such that aventrally or dorsally directed translatory force is applied to thefixation device in the area close to the knee.
 2. The device as claimedin claim 1, characterized in that the two bar arms of the lower-leg bardevice are able to swivel about the same swivel axis situated at thedistal end of the thigh bar.
 3. The device as claimed in claim 1,characterized in that the bar arms are coupled at their distal ends bymeans of bolts which extend laterally outward from the fixation device.4. The device as claimed in claim 1, characterized in that at least oneof the bar arms has, at its distal end, an oblong hole into which a boltof the fixation device protrudes, in order to couple the bar arm to thefixation device in a longitudinally displaceable manner.
 5. The deviceas claimed in claim 1, characterized in that the fixation device whichcan be secured on the lower leg is made up of a half-shell, and the twobar arms are coupled to the half-shell at the two opposite end areas ofthe half-shell.
 6. The device as claimed in claim 1, characterized inthat the spring device comprises a flat coil spring arranged in a springhousing which is secured on one of the bar arms and, together with thelatter, can be swiveled relative to the thigh bar, the center axis ofthe spring housing coinciding with the swivel axis.
 7. The device asclaimed in claim 6, characterized in that the pretensioning force of thespring device can be adjusted by means of a toothed wheel gear locatedin the spring housing.
 8. The device as claimed in claim 1,characterized in that the lower-leg bar device is mounted in an oblonghole of the thigh bar so as to be displaceable on the thigh bar.
 9. Thedevice as claimed in claim 8, characterized in that the oblong holeextends in the longitudinal direction of the thigh bar.